The invention concerns metal frames for spectacles.
Presently used techniques for making spectacle frames of NiTi alloys with a memorized shape, give the alloy a mild work-hardening treatment to facilitate processing, followed by heat treatment to memorize the shape and then further work-hardening to confer characteristics of elasticity in the range of temperatures at which the frames will be used, from xe2x88x9220xc2x0 C. to +40xc2x0 C.
A high rate of work-hardening would make the material fragile and it would then be impossible to obtain the complex forms needed for the spectacle frame components.
The above range of temperatures is in actual fact entirely inadequate. In very cold countries a temperature of xe2x88x9220xc2x0 C. is normal and, generally speaking, in mountainous areas temperatures lower than xe2x88x9220xc2x0 C. can be quite usual.
At 0xc2x0 C. the NiTi alloy is already less rigid and loses much consistency. At a lower temperature the spectacle frames can be bent even with very little pressure.
On account of the memorized shape and extreme elasticity, difficulties are encountered in adapting the frames to the faces of different users. Purpose of this invention is to overcome the above drawbacks and provide further considerable advantages as will now be explained.
Subject of the invention are spectacle frames having one or more components, such as the bridge, nose rests and ear pieces made of work hardened martenistic NiTi, NiTi niobium, NiTi iron alloys.
The components are made by plastic deformation starting from a 20% work-hardening of the alloy and then by hammering to reach about 50% making the ultimate section of the material, so stretched, sufficiently elastic and flexible, at temperatures ranging from xe2x88x9250xc2x0 C. to +70xc2x0 C., to make the frames adaptable to the different faces of users.